Hydrolysis of polylactide in aqueous media

摘要

In this study, two commercial polylactide (PLA) grades with different D-lactate contents were subjected to hydrolysis in neutral, acidic, and alkaline aqueous media at temperatures above the glass transition. We monitored the hydrolysis process by means of tracking the changes in the molecular weight distribution, weight loss, water uptake, and PLA crystallinity as a function of time. In both, neutral and acidic media, hydrolysis showed an initial induction period over which no weight loss was observed, whereas the average molecular weight dropped drastically. After this initial period, the weight loss increased rapidly, whereas the molecular weight decreased slowly. Additionally, in alkaline media, hydrolysis occurred mainly through a surface-erosion process; this resulted in a simultaneous molecular weight decrease and weight loss without a noticeable induction period. An autocatalytic mechanism was assumed in neutral and acidic media to describe the hydrolysis kinetics. The measured molecular weight decrease over time was successfully described by a two-stage exponential model. (C) 2016 Wiley Periodicals, Inc.